Manufacture of machinable molybdenum



F'b. 17, 1953 J. H. RAMAGE E'l'AL 2,628,926

MANUFACTURE OF MACHINEABLE MOLYBDENUM Filed June 21, 1949 2 SHEETS-SHEET 1 ATTORNEY Feb. 17, 1953 J. H. RAMAGE EI'AL MANUFACTURE OF MACHINEABLE MOLYBDENUM 2 SHEETS-SHEET 2 Filed June 21, 1949 AWQWM ATTORNEY Patented Feb. 17, 1 953 e UNITED STATES ATENT OF MANUFACTURE OF MACHINABLE MOLYBDENUM Application June 21, 1949, Serial No. 100,392

10 Claims. 1

This application is a continuation in part of the application, Serial No. 722,306, filed January 16, 1947, now abandoned.

This invention relates to molybdenum and, more particularly, to such that is easily machineable.

The principal object of our invention, generally considered, is to produce molybdenum in which, on an average, the length of each grain is no less than two and no more than four, or at the utmost for certain purposes, six times the width or diameter, whereby the material is easily machineable and, at the same time, the crystal cohesion is good and the material not too weak.

Another object of our invention is to produce molybdenum in which the grains are at least slightly elongated beyond a one to one ratio between lengths and widths, say on the average, to no less than two and generally no more than four times their transverse dimensions.

A further object of our invention is to produce molybdenum in which the grain size is between 10 and 250 per square millimeter, while the grain length is increased from an unworked or recrystallized condition, of a one to one ratio between the length and transverse dimensions, to avoid poor crystal cohesion and weak material, to not less than a grain length of two, and generally not more thana grain length of four, times the transverse dimension, thereby also avoiding long fibrous material which will not machine.

Other objects and advantages of the invention will become apparent as the description proceeds.

Referring to the drawing:

Figure 1 is a perspective view of a piece of molybdenum embodying our invention.

.Figure 2 is a perspective view of an ingot of molybdenum undergoing a rolling operation.

Figure 3 is a sectional view of a swaging machine through which a piece of molybdenum is being passed;

'Figure' l is a longitudinal sectional view of a furnace in which molybdenum may be sintered and/or recrystallized.

Figure 5 is a reproduction of a photomicrograph, at a magnification of 100, in the drawing accompanying the application, of an etched surface of a piece of readily-machineable molybdenum, embodying our invention.

,Figure 6.15, a reproduction of a photom1crograph, at a similar magnification, of an etched surface of a piece of molybdenum which is hard to machine.

Figure 7 is a reproduction of a photomicrograph, at a similar magnification, of a piece of molybdenum which is impossible to machine because the grains thereof are fibrous, that is, elongated to too great an extent.

It has been known that molybdenum can be machined only with great diificulty and even in the so-called machineable lots and single bars, a large percentage was found not machineable.

We have made a study of molybdenum which was found to be easily machineable, difficultly machineable, and practically unmachineable, and are able to now recognize the features that render it machineable and fabricate molybdenum that is uniformly machineable throughout.

We have found that it is essential, in easily machineable molybdenum, that the grain structure be such that in no direction is the length of the grains less than two or generally more than four times the width or diameter, on an average. However, the grain size has been found not to be restricted to a narrow range, as we have rendered molybdenum machineable over a range of 10 to 250 grains per square millimeter, which range includes most of the molybdenum used in industry.

Perfectly equiaxed grains, that is those in which the length corresponds with the transverse dimension or diameter, and occur in treated or cast metal, unworked mechanically, are not good because the crystal cohesion is poor so that the machining tool pulls whole grains out of the body of the metal beneath the actual-cut, leaving a pitted finish, and the material composed of such grains is too weak, resulting in cracks and breaks due to the stress of the tool.

On the other hand, molybdenum in which the fibres are long, as in a case where the metal has been rolled or drawn sufiiciently to make it duetile, will not machine at all. The tenacity of the long fibres breaks the tool tip, blunts the cutting edge, and results in fibres tearing out beyond the point of machining,

One method of producing easily machineable molybdenum in accordance with our invention, and with reference to the drawing in detail, is

to press under conventional or standard conditions, the powdered metal into a slug, bar, or,:

ingot II, which may be of a convenient size, an example being 1" x 1 /2" in section, and 24" long. Such a bar may then be placed in a furnace, such as represented by the reference character l2 and corresponding with that illustrated in Figure 1 of the Hall et al. Patent No. 2,431,690, dated December 2, 1947. In such a furnace it is desirably treated in accordance with the method disclosed in said application, thatis, it is heated to between about 1400 and 1700 C., or between 50% and 70%, or not more than 70% of that of fusion, as measured in degrees C., in a hydrogenbearing reducing atmosphere, containing enough water vapor so that a reversible oxidation-reduce tion reaction occurs, for a relatively long period of time, say about two, or from about 1 /2 to 3 hours, resulting in the desired sintering ofthe particles to produce a strong coherent article.

Such a bar during the sintering operation shrinks to a coherent metallic condition, the final dimensions being approximately /8 x 1 /4" x 20" long. The bar H produced may then be worked to develop the grains to the extent desired, that is, it may for example be passed between rollers I3 and I4, illustrated in Figure 2, after heating in a, furnace at a temperature between about l450-and 1500 C., and reduced to a bar II approximately }2-" square in section, that is about 60%. of its original section. The bar ll may then be passed through a swaging machine [5, after being taken from a furnace at a temperature of between 1350 and1450 C. and reduced to a rod W, .535 diameter in cross-section,

that is, about 34%, of its pre-swaging sectionand' about 21% of its original section. The rod ll so produced may then belplaced in the furnace 12 or another one and, in a protective or reducing atmosphere, recrystallized by holding 20 minutes or more at a temperature. of about 1600 C. It may then be swaged orotherwise worked to the desired size, at which the crystals are elongated on the averageto preferably no less than two and no more than four times their transverse dimensions. The scale formedmay be cleaned off in boiling caustic soda or potash.

' As analternative, such a pressed and sintered baror slug of molybdenum may, instead of bein reduced to a bar {-2 square in cross-section, may be rolled to one square in cross-section, that is, about 51% of its original section at a furnace temperature of1450 to 1500 C., then swaged to .636" round section, that is, about 56% of its pre-swaging section, and about 29% of its original section, at a furnace temperature of 1350 and 1400 C., and then recrystallized by heating for about 20 minutes or moreat about 1600 C. in a protective atmosphere. to .550 round, that is, with a reduction in area of about and not more than 25% and cleaned as by washing in boiling caustic.

Another example would be to treat as above by finishing to .550" round sectionbefore recrystallizing at 1600 C., after Whichjust enough workingis applied to avoid poor crystal cohesion and undesired weakness, not elongating the grains to more than four times their transverse dimensions on the average.

In the previous examples, we have obtained the desired elongation of the grains by a final working, after a reduction to about 21% in the first, and about. 29% in the second examplaofthe original cross-sectional area (a reduction in area ofrespectively about 79% and71% and heating torestoresaid grains to an equiaxed condition.

It is, however, possible to obtain this result with- It may then be swagedout a final working step, if a final heating step at a temperature above that of recrystallization is accurately controlled as to time and temperature, so that the grains, after undue elongation for easy machineability, are restored, not to an equiaxed condition, but to one in the desired range where easy machineability obtains.

In other words, instead of sintering, working, then recrystallizing at a predetermined size, to an equiaxedcondition, as: by heating for twenty minutes at a temperature of about 1600 C. and. finally working to the finished size and get the desired grain elongation, we may instead conclude. the treatment, after sintering the pressed powder and working to finished size, by annealing for one, or approximately one, hour per h" of section thickness at a recrystallizing temperature between l300 and l350 C., or about 1325 C., in order to eiiect a formation of the preferred recrystallization pattern so that the elongated grains are not restored entirely to an equiaxed condition, as previously, but only modified toward that condition, stopping when the grains are still elongated to an extent that is not less than twice their transverse dimensions, and not more than four, or at the extreme, six timestheirtrapsverse dimensionson the average,

Such treatment is p rticularly applicable; to

making molybdenum rods for drilling, and; eX-

ternal and internal threading, as, for examplerim making cathode supports in which diameter; holes are drilled 25% deep, using. highv Speed carbon steel drills. Prior. to our invention, a, drill was first employed followedby, aria 0111111..

However, when, treating the molybdenum in ace:

cordancewith our invention so that. it iseasily. machineable, we now initially drill the holewith ease, using a T g" drill.

Also we have foundthat, using. lightcutsand .slow speeds, it is. possible to externally thread such a molybdenum rodforming, for example, 30 threads per inch without. difficulty by meanslof a tool bit and chaser. Theresulting threadsare relatively sharp and clean, as comparediwithpriorpractice in which only imperfect threads, were obtainable.

Using a 20 thread per inch die, we have ob.-.

tained sharp cleanthreads on, rods, formed of;

machineable molybdenum in accordance without invention, as contrasted with molybdenum not so treated, Where only roughand broken threads. Were obtainable.

We have also tapped machineablemolybdenumin accordance with our invention, producing 32':

threads per inch with ease, whereas, non

machineable molybdenum. in: accordance. with.

prior practice could not be sotapped.

Figure 5 is a reproduction of a photomicroe. graph which represents easily machineable .molybdenum, that is, in. which the. grains are slightly elongated to about but notmorethan. four times their transverse dimensions, on the average. molybdenum in which the grains are elongated to morethan six times theiraverage transverse, dimensions, but not to an extreme. condition where very fibrous material is obtained. The metal represented by this figureis machineable only with difiiculty.

Figure 7 shows, for comparison; molybdenum which has been worked or drawn to an excessive extent to elongate the grains or-crystals in the. This; material will not machine at' all, because the.

direction of working to make it=d1ictile.

tenacity of'the long-fibresbreaks the toolitips,

Figure 6, on the other hand, representsblunts the cutting edge, and causesfib'res to tear out beyond the point of machining.

From the foregoing disclosure, it will be seen that we have devised a method for producing molybdenum which is readily machineable, and such readily machineable molybdenum. Variations in the method within the scope of our invention, in which the desired final crystal structure is provided, are permissible. In producing thin sections, such for example as represented in Figure l by the reference character H, it is usually desirable to have some further working, after the recrystallization treatment, to increase the strength and ductility of the metal so that it will resist, without failure, stress as applied bythecutting tool;

It is to be understood that all of the specified rolling and swaging operations elongate the crystals in the direction of the working operation, and that subsequent heating for the next operation must be such as to break up the grains toward the equiaxed condition again until near the finished size, when a slight amount of elongation, usually not to exceed four to one, or at most six to one, on the average, is desired for strength and ductility. This requires that the furnace temperatures for heating prior to working steps be high enough to remove previous elongation, or that a separate recrystallization step be instituted at some point in the process, preferably near the finish. The point this step should be interposed will be determined by the size to which the material is to be finished.

Although a preferred embodiment of our uniformly free machineable type of molybdenum and process of manufacture has been disclosed, it will be understood that modifications may be made within the spirit and scope of the appended claims.

We claim:

1. The method of producing easily machineable molybdenum comprising rolling a bar about 7 x 1%," in cross-section of that material sintered from the pressed powder to about l-" square in cross-section at a temperature between about 1450" and 1500 C., swaging said bar to about .535" diameter in cross-section at a temperature between about l350 and 1400 C., recrystallizing by heating at about 1600 C. for about twenty minutes in a protective atmosphere, and then swaging to a desired size at whichthe crystals are elongated on the average to no less than two and no more than four times their transverse dimensions.

2. The method of producing easily machineable molybdenum comprising rolling a bar about 7 x 1%" in cross-section of that material sintered from the pressed powder to about square in cross-section, at a temperature between about 1450 and 1500 C., swaging to about .636" diameter in cross-section at a temperature between about 1350 and 1400 C., recrystallizing by heating at about 1600 C. for about twenty minutes in a protective atmosphere, and then swaging to a cross-section of about .55" diameter.

3. The method of producing easily machineable molybdenum comprising rolling a bar about 7 x 1 /4 in cross-section of that material sintered from the pressed powder to about .550" diameter in cross-section at a temperature between about 1450 and 1500 C., recrystallizing by heating at about 1600? C. for about twenty minutes in a protective atmosphere, and then working just enough to avoid poor crystal ooheslon and undesired weakness, elongating therains to no less than two and no more than four times their transverse dimensions on the average.

4. The method of producing molybdenum comprising rolling and swaging a bar thereof sintered from the powder at temperatures between about 1350 C. and 1500 C., to reduce it in section and elongate its grains to produce a fibrous structure, recrystallizing said bar by heating at about 1600 C., and finally swaging to reduce the transverse sectional area of said bar about and not more than 25% at which the grains are elongatedso that the ratio between length and transverse dimension lies between only slightly more than one to one and that where the grain lengths are six times their transverse dimensions, on the average, in order to make the material easily machineable, the exact grain length to width ratio depending on the strength desired in the metal,

which strength increases with increase in lengthwidth ratio.

5. The method of producing molybdenum comprising rolling and swaging a bar thereof, sin-tered from the powder, at temperatures between about 1350 C. and 1500 C., to reduce it not more than about 79% in section and elongate its grains to produce a fibrous structure, recrystallizing said bar by heating at about 1600 C., and finally working to reduce the transverse sectional area of said bar about and not more than 25%, thereby elongating the grains, on the average, to between two and six times their transverse dimensions, by said working, in order to make the material easily machineable.

6. The method of producing easily machineable molybdenum, comprising; first, the rolling and swaging of a sintered bar thereof at temperatures between about 1350 C. and 1500 C., to produce a fibrous structure; second, the recrystallization of said bar, as by heating at about 1600 C. and; third, the reduction in transverse sectional area of about and not more than 25%, to produce grains which are, on the average, not less than about twice as long as their transverse dimensions, to overcome poor crystal cohesion and undesired weakness and which are, on the average, not more than four times as long as their transverse dimensions.

7. The method of producing easily machineable molybdenum comprising rolling a bar about x 1 in cross-section of that material sintered from the pressed powder, at a temperature between about 1450 C. and 1500 C., to about {-3" square in section, swaging said bar at a slightly lower temperature to about .535 diameter in section, producing a fibrous structure, heattreating at about 1600 C. to recrystallize the material, and then working to reduce its transverse sectional area about and not more than 25%, thereby elongating the grains to, on the average, no less than two and no more than four times their transverse dimensions.

8. The method of producing easily machineable molybdenum comprising rolling a bar about 3 8" x 1%" in cross-section of that material sintered from the pressed powder, at a temperature between about 1450 C. and 1500 C. to about A" square in cross-section, swaging said bar at a slightly lower temperature to about .636" diameter in cross-section, producing a fibrous structure, recrystallizing at about 1600 C., and swaging to a cross-section of about .550" diameter.

9. The method of producing easily machineable molybdenum comprising rolling a bar of that material. sint'eredtfrom the. pressed 'po'wder to: a; smaller cross-section at. a temperature between about 11450 C. and 1500C., to elongate itsrgrains to more than six times their transverse dimensions.to= produce a fibrous structure, and heating to a.recrystallizing. temperature between" 1300" C. and 1350 C'. for approximately onehour per A of "section thickness, to merely modify the grains toward an equiaxed condition, stopping, however; when. the grains are still elongated, on the aver-- age, to an extentxthat is not less than twice, and not more than six times their transverse dimensions;

1 0; The method of producing easily machineable-molybdenum comprising working to finished sizeabar sint'ered from the powder to elongate its-grainsto more than six times their transversedimensions to a fibrous condition, and concluding the treatment by annealing for approximately one hour per fl of section thickness at a temperaturebetween 1 300 C; and 1350 C., in order to effectaformation of the preferred recrystallizatiorr. pattern, where: the elongated grains: are

not restored entirely" to. an equiaxed condition, but:sti11e1ongated to; an extent, that. is, on the average; not-less: than twice and not more, than four times theirtransverse dimensions.

THEL BLOOMFIELD BANK AND TRUST COu,

By A. ELLIS,

Vice: President and Trust Ojficer, Executor'oj'theLast Will. and Testament of John H.1Ramage; Deceased.

ROBERT D. MALIN;

REFERENCES CITED The following references are of record in the file of this patent:

UNITED. STATES:v PATENTS Number Name Date 1,635fl93 Koref et a1 'Ju1y'12-, 1927' 1,891,050 Laise' Dec. 13, 1932 2,300,353: Eberhardt Oct; 27, 1942' 

5. THE METHOD OF PRODUCING MOLYBDENUM COMPRISING ROLLING AND SWAGING A BAR THEREOF, SINTERED FROM THE POWDER, AT TEMPERATURES BETWEEN ABOUT 1350* C. AND 1500* C., TO REDUCE IT NOT MORE THAN ABOUT 79% IN SECTION AND ELONGATE ITS GRAINS TO PRODUCE A FIBROUS STRUCTURE, RECRYSTALLIZING SAID BAR BY HEATING AT ABOUT 1600* C., AND FINALLY WORKING TO REDUCE THE TRANSVERSE SECTIONAL AREA OF SAID BAR ABOUT THE NOT MORE THAN 25%, THEREBY ELONGATING THE GRAINS, ON THE AVERAGE, TO BETWEEN TWO AND SIX TIMES THEIR TRANSVERSE DIMENSIONS, BY SAID WORKING, IN ORDER TO MAKE THE MATERIAL EASILY MACHINEABLE.
 10. THE METHOD OF PRODUCING EASILY MACHINEABLE MOLYBDENUM COMPRISING WORKING, TO FINISHED SIZE A BAR SINTERED FROM THE POWDER TO ELONGATE ITS GRAINS TO MORE THAN SIX TIMES THEIR TRANSVERSE DIMENSIONS TO A FIBROUS CONDITION, AND CONCLUDING THE TREATMENT BY ANNEALING FOR APPROXIMATELY ONE HOUR PER 1/4" OF SECTION THICKNESS AT A TEMPERATURE BETWEEN 1300* C. AND 1350* C., IN ORDER TO EFFECT A FORMATION OF THE PREFERRED RECRYSTALLI- 